The present invention relates to the field of implanatable medical devices. More particularly, the present invention relates to cardiac pacing systems having venticular fusion prevention.
Implantable cardiac pacing systems such as implantable pulse generators (IPGs) are well-known in the art. Implantable cardiac pacing systems deliver a pacing signal to stimulate a heart chamber. The pacing signal is typically delivered by an electrode in the heart chamber. The same electrode is also used to sense electrical activity indicating an intrinsic contraction of the heart chamber. The presence or absence of the sensed contraction, and the timing of the contraction, are used to control the cardiac pacing system for the patient""s well being.
The sensing electrodes can only sense electrical activity near the small tip of the electrode, however. Electric activity may have started in the heart chamber, but not yet have reached the sensing electrode. For example, the tip of the ventricular electrode is typically located in the apex of the right ventricle. The ventricular electric wave front may have left the AV node and be on the way to the apex, but the ventricular electrode will not know that any activity has occurred until the electric wave front reaches the sensing site in the apex.
Because the pacing system is unaware that the electric wave front is on its way, it may generate an unnecessary ventricular pace, even though the intrinsic ventricular wavefront would have occurred momentarily. The ventricular pace results in a fusion beat, here defined as a ventricular pace delivered when the ventricle is already contracting by an intrinsic contraction. This type of fusion beat wastes battery energy, reducing the battery life, and interferes with the patient""s own intrinsic heart rhythm, which is preferred over the pacing system imposed rhythm.
Fusion pacing could be reduced by providing a ventricular sensing electrode closer to the AV node, but the ventricular electrode is typically located in the apex of the right ventricle. Another signal indicating ventricular activity is the Far Field R-Wave (FFRW) sensed in the atrium. Atrial leads are present in DDD and VDD devices. The Far Field R-Wave (FFRW) is a product of ventricular depolarization sensed in the atrium by the atrial electrode. xe2x80x9cFar Field R-Wave Classification by Signal Form,xe2x80x9d by Westendorp et al., PACE, Vol. 22, June 1999, Part II, P218, page A100, reports that FFRWs originating from intrinsic ventricular contractions can be sensed by the atrial lead up to 25 ms before the ventricular contraction has been sensed by the ventricular lead, depending on the position of the atrial and ventricular leads. In current pacemakers, the FFRW is often blanked with an atrial blanking window to avoid mistaking it for a real atrial event. This atrial blanking window prevents using the FFRW as an early indication of ventricular contraction.
U.S. Pat. No. 5,999,853 to Stoop et al. discloses a dual chamber pacing system for cardiac pacing, preferably a system with a single pass lead providing at least one ring electrode positioned in the patient""s atrium, and at least a distal tip electrode for positioning in the patient""s right ventricle. At least three signals are selected cyclically for concurrent processing, e.g., the AR signal, atrial ring to can; the VT signal, ventricular tip to can; and RT, atrial ring to ventricular tip. In addition, a second spaced ring can be positioned in each of the atrium and ventricle, for bipolar sensing in each of those heart chambers. In a preferred embodiment, each sensed signal is digitized and processed through the digital signal processor for comparing the patterns of the respective signals, as well as the respective timing of the signals. Based on the pattern and/or timing processing, the concurrent signals are interpreted to represent a P-wave, R-wave or xe2x80x9cother,xe2x80x9d where other may be simply noise, a far field R-wave, or an ectopic beat.
U.S. Pat. No. 5,755,739 to Sun et al. discloses an adaptive and morphological method and system comprising two basic steps. In the first step, an adaptive filtering stage using an R-wave correlated reference (R-Trigger) that removes undesirable R-waves and high amplitude T-waves from the A-EGM signal. The use of R-wave time position sequence or higher order sequence as the reference input signal in the adaptive filter stage significantly enhances the processing speed. In the second step, morphology analysis of the adaptively filtered A-EGM is conducted to detect the P-waves in the adaptive filter output error signal only when atrial channel trigger (P/R-Trigger) signals are detected in the A-EGM. This reduces the amount of time that morphology computation is conducted in the cardiac cycle, thereby reducing computational complexity and allowing real time analysis of the A-EGM in an implantable cardiac stimulator or monitor.
U.S. Pat. No. 5,534,016 to Boute discloses a pacemaker having an algorithm for varying the AV escape interval and detecting when the AV delay is lengthened to the point of evoking a fusion beat, thereby providing an accurate indication of a patient""s underlying PR interval without significant loss of pacing capture. By monitoring T-wave detection and drop in amplitude of the evoked T-wave, an algorithm is enabled for optimizing the pacemaker AV delay within a range of values just less than the longest value for obtaining pre-excitation by the delivered pace pulse.
U.S. Pat. No. 4,825,870 to Mann et al. discloses a pacemaker that monitors the heart to detect crosstalk, defined as any signals sensed within a predetermined interval following the atrial stimulation pulse. If crosstalk is detected, the pacemaker follows with a ventricular stimulation pulse at the end of the AVI (which AVI assumes one of two values depending upon whether crosstalk was detected) following the atrial pulse unless a normal ventricular activity is sensed, in which case the ventricular stimulation pulse is inhibited.
U.S. Pat. No. 4,365,639 to Goldreyer discloses a cardiac pacemaker with a single catheter for insertion into a heart through the vascular system. An electrode system for the catheter including a stimulating electrode at the distal end of the catheter for positioning at the apex of the right ventricle, with the stimulating electrode connected to the pulse generating unit of the pacemaker, and sensing electrodes on the catheter spaced from the stimulating electrode for positioning adjacent to the wall of the right atrium for sensing signals generated by the atrial excitation or P-wave, with the P-wave signals connected as input to the pacemaker for determining the timing of the ventricular stimulating pulses. The sensing electrodes are circumferentially equidistant from the stimulating electrode and provide one or more bipolar signals for the pulse generating unit. In alternative configurations, the stimulating electrode and the sensing electrodes are positioned in various locations within the heart to provide other methods of cardiac control.
The most pertinent prior art publications known at the present time are shown in the following table:
All publications listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.
The present invention is therefore directed to providing a system and method for ventricular fusion prevention. The system of the present invention overcomes the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of ventricular fusion prevention.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art ventricular fusion prevention. Those problems include, without limitation: (a) unnecessary battery use from applying a ventricular pace when the intrinsic contraction is already present, (b) ventricular pacing interference with the intrinsic ventricular wavefront, (c) need for ventricular fusion prevention, (d) need for max AV interval adjustment if too many fusion beats are occurring, and (e) uncertainty in electrode placement.
In comparison to known techniques for ventricular fusion prevention, various embodiments of the present invention provide one or more of the following advantages: (a) increased battery life, (b) reduced interference with the intrinsic heart rhythm, and (c) max AV interval adjustment.
Some of the embodiments of the present invention include one or more of the following features: (a) an IMD having ventricular fusion prevention using Far Field R-Wave detection to indicate ventricular contraction, (b) an IMD having ventricular fusion prevention without requiring FFRW form analysis, (c) an IMD having max AV interval adjustment, (d) methods of ventricular fusion prevention, and (e) methods of max AV interval adjustment.
At least some embodiments of the present invention involve starting the fusion beat prevention method when the AV timer has reached the max AV interval and a ventricular pace is scheduled. The activity of the last wait time, defined as a typical time between sensing an intrinsic ventricular contraction at the atrial lead and sensing an intrinsic ventricular contraction at the ventricular lead, is checked to see if atrial activity (Asense) has occurred. If atrial activity was not sensed in the preceding wait time, a ventricular pace is applied immediately because no fusion beat is expected.
If atrial activity was sensed in the preceding wait time, a fusion beat is still possible so the system waits for a ventricular sense (Vsense) to occur or for an additional wait time to elapse. If a ventricular sense occurs, the scheduled ventricular pace is cancelled to avoid a fusion beat. If the wait time elapses without a ventricular sense, a ventricular pace is administered.
Other embodiments of the present invention involve incrementing a fusion beat counter when a ventricular pace is cancelled because a fusion beat would have occurred. When the fusion beat counter reaches a predetermined value, the max AV interval can be increased to give the intrinsic rhythm more chance to occur.